Transcranial magnetic stimulation output circuit and control method thereof

Abstract

This invention discloses a transcranial magnetic stimulation (TMS) output circuit and its control method, comprising a main charging / discharging pulse generation circuit, a charging compensation circuit, and a thyristor protection circuit. The main charging / discharging pulse generation circuit includes a charging capacitor C1, a helmet coil L1, a charging drive transistor Q2, and a capacitor discharge thyristor T1. The charging compensation circuit includes compensation capacitors C2 and C3, and a resistor R4. The compensation capacitor C3 is connected in parallel across the helmet coil L1, and the compensation capacitor C2 and resistor R4 are connected in series and then in parallel across the capacitor discharge thyristor T1. The thyristor protection circuit includes a thyristor protection device Q1, resistors R1, R2, and R3. The resistors R1, R2, Q1, and R3 are connected in series and then in parallel across the capacitor discharge thyristor T1. Using this invention, the rate of change of current dI / dt along the pulse rise edge can be increased, allowing the magnetic pulse signal to act more effectively on intracranial nerve cells or fibers, thus enhancing the therapeutic effect on diseases such as depression.

Description

Technical Field

[0001] This invention belongs to the field of transcranial magnetic stimulation, and in particular relates to a transcranial magnetic stimulation output circuit and its control method. Background Technology

[0002] The mechanism of transcranial magnetic stimulation (TMS) is mainly to generate a volume electric field in the skull by passing a magnetic field through the skull, which induces the generation of current in the brain's nerve cells. By changing the amplitude and frequency of the magnetic stimulation, it aims to excite or inhibit the function of brain nerve cells.

[0003] For example, Chinese patent document CN112827065A discloses a transcranial magnetic stimulation system, which rapidly releases the charge of the energy storage capacitor in the main motor box, and passes a pulse current through the stimulation coil placed above the head, thereby generating a pulsed magnetic field around the stimulation coil. The magnetic lines of force penetrate the skin and skull to the brain nerves with little resistance without trauma, generating a conductive induced current in the cranium.

[0004] Chinese patent document CN107362450A discloses a transcranial magnetic stimulation circuit, including: at least two inductor coils, a DC power supply, a charging circuit and a discharging circuit for the inductor coils, and a controller. The controller controls the at least two inductor coils to synchronously generate magnetic pulses through an electronic switch.

[0005] Transcranial magnetic stimulation (TMS) is widely used internationally for the treatment of depression. However, no TMS devices have been approved for use in the treatment or adjunctive therapy of depression in China. Meanwhile, TMS technology has also been extensively studied in the relief and treatment of sleep disorders, central pain, drug addiction, and Alzheimer's disease. Many studies indicate that the steepness of the rising edge of the TMS pulse (dI / dt) is positively correlated with the magnitude of the induced current generated after magnetic stimulation of intracranial nerve cell bodies or fibers, i.e., positively correlated with the therapeutic effect of the TMS device.

[0006] With the development and application of transcranial magnetic stimulation (TMS) technology, there is room for further improvement in the current change rate dI / dt of TMS pulses. However, since the load of the pulse output is an inductive device, the thyristor, the core component of the TMS output circuit, is susceptible to breakdown damage due to the forward and reverse overshoot voltages generated under high-power inductive loads. This is especially true when the pulse width is relatively small, such as less than 300µs (a smaller pulse width helps reduce the heating of the inductive load L, which is coiled and placed on the patient's head). In these cases, suppressing the forward and reverse overvoltage peaks of the thyristor becomes crucial, directly impacting the equipment's lifespan, reliability, and failure rate. Summary of the Invention

[0007] This invention provides a transcranial magnetic stimulation output circuit that can increase the value of the pulse rise edge current change rate dI / dt, so that the magnetic pulse signal can act more effectively on intracranial nerve cells or fibers, thereby enhancing the therapeutic effect on diseases such as depression; at the same time, it can improve the lifespan and reliability of the device and reduce the failure rate.

[0008] A transcranial magnetic stimulation output circuit includes a main charging and discharging pulse generation circuit, a charging compensation circuit, and a thyristor protection circuit.

[0009] The main charging and discharging pulse generating circuit includes, in series, a positive power supply terminal, a current transformer B1, a charging capacitor C1, a current transformer B2, a helmet coil L1, a resistor R6, a charging start-up drive transistor Q2, and a negative power supply terminal; the end of the resistor R6 closest to the positive power supply terminal is connected to the cathode of the capacitor discharge thyristor T1, and the end closest to the negative power supply terminal is connected to the anode of the diode D1; both the anode of the capacitor discharge thyristor T1 and the cathode of the diode D1 are connected to the positive power supply terminal.

[0010] The charging compensation circuit includes a compensation capacitor C2, a compensation capacitor C3, and a resistor R4; wherein, the compensation capacitor C3 is connected in parallel across the two ends of the helmet coil L1, and the compensation capacitor C2 and the resistor R4 are connected in series and then in parallel across the two ends of the capacitor discharge thyristor T1.

[0011] The thyristor protection circuit includes a thyristor protection device Q1, a resistor R1, a resistor R2, and a resistor R3; wherein, the resistors R1, R2, the thyristor protection device Q1, and the resistor R3 are connected in series and then in parallel to the two ends of the capacitor discharge thyristor T1.

[0012] This invention improves the charging compensation of the charging capacitor C1 to the helmet coil L1 by setting a charging compensation circuit, making the rise time of the L1 current faster and the dI / dt value larger; it makes the magnetic pulse signal act more effectively on the intracranial nerve cell body or fiber, enhances the intensity of the induced current generated by the neuronal cells and fibers after magnetic stimulation, or is equivalent to increasing the sensitivity of neuronal cell excitation, thus enhancing the effect of transcranial magnetic stimulation therapy and increasing the stimulation depth of magnetic stimulation in the cranium.

[0013] Meanwhile, a thyristor protection circuit was designed to protect the capacitor discharge thyristor T1 in the output circuit, preventing breakdown caused by the forward and reverse overshoot voltages generated by the thyristor T1 under high-power inductive loads.

[0014] Furthermore, the charging compensation circuit also includes a diode D2 and a resistor R5, which are connected in series and then in parallel across the resistor R4; wherein, the anode of the diode D2 is connected to the positive terminal of the power supply, and the cathode of the diode D2 is connected to one end of the resistor R5.

[0015] Furthermore, the input circuit of the thyristor protection detection circuit OPT1 is connected in parallel across the two ends of the resistor R1. OPT1 is an optocoupler used to electrically isolate the voltage signal across R1 before transmitting the signal across R1 to the microcontroller (MCU).

[0016] The present invention also provides a control method for a transcranial magnetic stimulation output circuit, which, when using the above-mentioned transcranial magnetic stimulation output circuit, includes:

[0017] During charging, a driving voltage is first applied to the control terminal of the charging start-up drive transistor Q2. After the charging start-up drive transistor Q2 is turned on, the charging capacitor C1 is charged by +V and -V. When the charging is finished, the charging start-up drive transistor Q2 is turned off, and the induced voltage of the helmet coil L1 charges the compensation capacitor C3 and the charging capacitor C1.

[0018] When the energy discharge of the helmet coil L1 ends, the compensation capacitor C3 releases energy to L1; after 1 / 4 of the resonance cycle of L1 and C3, an on-control signal is applied to the capacitor discharge thyristor T1, and the capacitor discharge thyristor T1 is turned on, and the charging capacitor C1 will discharge to the helmet coil L1 through the capacitor discharge thyristor T1.

[0019] By controlling the turn-on time of the capacitor discharge thyristor T1 to match the discharge time of the compensation capacitor C3, the compensation capacitor C3 and the charging capacitor C1 discharge superimposedly on the helmet coil L1, forming a steep pulse with a combined current rising edge on the helmet coil L1.

[0020] When the capacitor discharge thyristor T1 is about to turn on, an activation control voltage is applied to the gate of the thyristor protection device Q1 to turn it on. The conduction time of the thyristor protection device Q1 is slightly longer than that of the capacitor discharge thyristor T1. After the thyristor protection device Q1 turns on, resistors R1, R2, and R3 are connected in parallel across the capacitor discharge thyristor T1 to absorb the positive and negative overvoltage peak pulses of the capacitor discharge thyristor T1.

[0021] The charging and discharging current on the charging capacitor C1 is led out through the secondary terminal Ciout of the current transformer B1 connected in series in the circuit of the charging capacitor C1; the current led out through the secondary terminal Ciout of the current transformer B1 is obtained by linear rectification and smoothing circuit to obtain the current detection when the charging capacitor C1 discharges to the helmet coil L1, which is used for real-time current sampling and overcurrent protection sampling signal when the helmet coil L1 is working.

[0022] The charging and discharging current on the helmet coil L1 is led out through the secondary terminal Liout of the current transformer B2 connected in series in the helmet coil L1 circuit; the current led out through the secondary terminal Liout of the current transformer B2 is converted as the current, time and phase detection of the inductance of the helmet coil L1.

[0023] In this invention, the pulse width of the magnetic stimulation of the circuit is 280µs. This pulse width is determined by 1 / 4 of the resonance period of L1 and C3 + one resonance period of L1 and C1 + the damping circuit after the end of one resonance period of L1 and C1. With a smaller pulse width, the heating of the helmet coil L1 is reduced.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] 1. In the output circuit of this invention, the pulse width of the magnetic stimulation is 280µs, which is narrower than the pulse width of a typical transcranial magnetic stimulation (TMS) device. This effectively reduces the heat generated by the helmet coil and also improves the safety of the dosage during TMS stimulation.

[0026] 2. By designing a charging compensation circuit, this invention improves the dI / dt value when the high-voltage capacitor discharges to the helmet coil, thereby increasing the sensitivity of intracranial nerve cells or nerve fibers to magnetic stimulation, improving the efficiency of magnetic stimulation inducing nerve cell current, and increasing the stimulation depth of the magnetic field pulse in the intracranial cavity.

[0027] 3. When the thyristor operates in a relatively narrow pulse, there is a risk of damage to the thyristor due to high-voltage forward and reverse peak voltages. This invention designs a thyristor protection circuit that protects the thyristor from forward and reverse overvoltage peaks, thereby improving the thyristor's operational stability and reliability.

[0028] 4. The transcranial magnetic stimulation device of the present invention can sample and control the current in the helmet coil and the current when the high voltage capacitor discharges to the helmet coil in real time during operation. Attached Figure Description

[0029] Figure 1 This is a circuit diagram of a transcranial magnetic stimulation output circuit according to the present invention;

[0030] Figure 2 This is a graph showing the relationship between the current and time on the helmet coil L1 in this invention. Detailed Implementation

[0031] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be noted that the embodiments described below are intended to facilitate the understanding of the present invention and do not constitute any limitation thereof.

[0032] like Figure 1 As shown, a transcranial magnetic stimulation output circuit includes a main charging and discharging pulse generation circuit, a charging compensation circuit, and a thyristor protection circuit.

[0033] The main charging and discharging pulse generating circuit includes the positive terminal of the power supply, current transformer B1, charging capacitor C1, current transformer B2, helmet coil L1, resistor R6, charging start drive transistor Q2, and negative terminal of the power supply connected in series. The end of resistor R6 closest to the positive terminal of the power supply is connected to the cathode of capacitor discharge thyristor T1, and the end closest to the negative terminal of the power supply is connected to the anode of diode D1. The anode of capacitor discharge thyristor T1 and the cathode of diode D1 are both connected to the positive terminal of the power supply.

[0034] The charging compensation circuit includes compensation capacitors C2 and C3, and resistor R4. Compensation capacitor C3 is connected in parallel across the helmet coil L1. Compensation capacitor C2 and resistor R4 are connected in series and then in parallel across the capacitor discharge thyristor T1. Diode D2 and resistor R5 are connected in series and then in parallel across resistor R4. The anode of diode D2 is connected to the positive terminal of the power supply, and the cathode of diode D2 is connected to one end of resistor R5.

[0035] The thyristor protection circuit includes a thyristor protection device Q1, resistors R1, R2, and R3. Resistors R1, R2, Q1, and R3 are connected in series and then in parallel across the capacitor discharge thyristor T1. A thyristor protection detection circuit OPT1 is connected in parallel across resistor R1.

[0036] During charging, a drive voltage is first applied to the control terminal of Q2, turning Q2 on and charging capacitor C1. The charging circuit is +V → F of current transformer B1 → G → C1 → B2 of current transformer → L1 → R6 → C terminal of Q2 → E terminal of Q2 → -V. During charging, the D terminal of charging capacitor C1 is positive and the E terminal is negative. The induced voltage of helmet coil L1 is positive at the B terminal and negative at the A terminal. When charging ends, Q2 is turned off. Since the current across L1 cannot change abruptly, the induced voltage generated by L1 is positive at the A terminal and negative at the B terminal. This induced voltage of L1 charges C3 and C1 through R6 and D1. The voltage polarity is positive at the W terminal of C3 and negative at the U terminal of C3. Due to the unidirectional conduction characteristic of D1, the positive voltage at the D terminal of C1 does not affect the positive voltage at the W terminal of C3. When the energy discharge of L1 ends, C3 will release energy to L1 in the reverse direction, with the W terminal positive and the U terminal negative; the current flows from terminal A to terminal B of L1. If at this time, an on-state control signal is applied to the capacitor discharge thyristor T1, T1 will conduct, and C1 will discharge to L1 through T1. Since L1 has just received a discharge from C3, due to the high resonant frequency of L1 and C3 (C3 has a relatively small capacitance) and the short discharge time τ, L1 will have a very narrow, steep rising pulse. The discharge current direction of C1 is from terminal D of C1 → T1 → terminal A of L1 → terminal B. If the on-state time of T1 is well-matched with the discharge time of C3, the superimposed discharge of both capacitors C3 and C1 to L1 will form a steep pulse with a combined current rising edge on L1. See... Figure 2The ab phase.

[0037] When the capacitor discharges and the thyristor T1 is about to turn on, a control voltage is applied to the gate of the thyristor protection device Q1 to turn it on (Q1's on-time is slightly longer than T1's, making the protection of T1 more reliable). This is equivalent to resistors R1, R2, and R3 being connected in parallel across T1 to absorb the forward and reverse overvoltage peak pulses of T1. (If only RC components are connected in parallel across T1 for peak pulse absorption, the energy release of the capacitor requires a long discharge time, and when the transcranial magnetic pulse frequency increases (τ decreases), the protection of the thyristor by pure RC components will be insufficient). This protection circuit can effectively reduce the risk of the thyristor being broken down by forward and reverse overvoltage peak pulses.

[0038] The discharge of capacitor C1 to L1 is a damped LCR charging and discharging circuit. As stated above, C1 discharges to L1, with the current direction being: upper terminal D of capacitor C1 → B1 → conducting capacitor discharge thyristor T1 → upper terminal A of L1 → E of C1. After the current in L1 reaches its maximum value, the induced electromotive force of L1 reverses, with terminal A becoming negative and terminal B becoming positive, charging capacitor C1. Because terminal A of L1 is negative, and the cathode of T1 is connected to terminal A, T1 remains conducting. The current in L1 gradually decreases to zero, see... Figure 2 Phase bc. Next, C1 discharges in reverse through L1. At this time, the capacitor discharge thyristor T1 is reverse-biased and automatically cuts off. A little later, the control electrode of Q1 is turned off, and Q1 also turns off. The reverse voltage of C1 charges L1 through diode D1 and resistor R6. When the reverse discharge of capacitor C1 ends, the current of L1 reaches its negative maximum value, as shown in phase cd. Then, the induced electromotive force of L1 reverses again, with terminal A of L1 positive and terminal B negative. Terminal A of L1 directly charges C3 on one hand, and charges C1 through R6 and D1 on the other. As the charging of both capacitors by L1 ends, the current of L1 drops to zero, and the voltage across C1 and C3 reaches its positive maximum value, as shown in... Figure 2 During this phase, C3 discharges through L1. Simultaneously, since T1 is off and D1 is reverse-biased, the voltage across C1 can only discharge through diode D2, resistor R5, and C2 to L1. Because the capacitance of C2 and C3 is much smaller than that of C1 (but their capacitive reactance is much larger), the effective discharge of C3 is the primary factor in the discharge to L1. See... Figure 2 The ef phase occurs. Then, the damped oscillation of L1 on C3 is absorbed by the C2, R5, D2, and C1 circuit. The pulse width of the entire transcranial magnetic stimulation is set to 280µs, waiting for the next Q2 conduction to repeat the new cycle.

[0039] The thyristor protection detection circuit consists of OPT1. When Q1 is turned on, current flows through R1, creating a voltage across R1. This voltage reflects the overvoltage peak voltage across the thyristor. This indicates that the helmet coil L1 is connected to the circuit. Q1 can also be activated briefly during the instrument's self-test to check if the helmet coil is disconnected from the machine. Its working principle is that when the helmet coil is connected to the machine, current flows through the R1 branch of Q1. This current is converted through the resistor R1, and the signal is transmitted to the microcontroller (MCU) via a high-voltage optocoupler (10,000 volts withstand voltage).

[0040] The charging and discharging current on capacitor C1 is drawn from the secondary terminal Ciout of current transformer B1, which is connected in series in the C1 circuit. Similarly, the charging and discharging current on L1 is drawn from the secondary terminal Liout of current transformer B2, which is connected in series in the L1 circuit. The current drawn from Liout can be converted to detect the current, time, and phase on the L1 inductor. The current drawn from the secondary terminal Ciout of current transformer B1 in the C1 circuit, after passing through a linear rectification and smoothing circuit, can be converted to obtain the current detection when high-voltage capacitor C1 discharges to helmet coil L1. This is used for real-time current sampling and overcurrent protection sampling signals when helmet coil L1 is working.

[0041] The embodiments described above provide a detailed explanation of the technical solutions and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, additions, and equivalent substitutions made within the scope of the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A transcranial magnetic stimulation output circuit, characterized in that, This includes the main charge / discharge pulse generation circuit, the charging compensation circuit, and the thyristor protection circuit; The main charging and discharging pulse generating circuit includes, in series, a positive power supply terminal, a current transformer B1, a charging capacitor C1, a current transformer B2, a helmet coil L1, a resistor R6, a charging start-up drive transistor Q2, and a negative power supply terminal; the end of the resistor R6 closest to the positive power supply terminal is connected to the cathode of the capacitor discharge thyristor T1, and the end closest to the negative power supply terminal is connected to the anode of the diode D1; both the anode of the capacitor discharge thyristor T1 and the cathode of the diode D1 are connected to the positive power supply terminal. The charging compensation circuit includes a compensation capacitor C2, a compensation capacitor C3, and a resistor R4; wherein, the compensation capacitor C3 is connected in parallel across the two ends of the helmet coil L1, and the compensation capacitor C2 and the resistor R4 are connected in series and then in parallel across the two ends of the capacitor discharge thyristor T1. The thyristor protection circuit includes a thyristor protection device Q1, a resistor R1, a resistor R2, and a resistor R3; wherein, the resistors R1, R2, the thyristor protection device Q1, and the resistor R3 are connected in series and then in parallel to the two ends of the capacitor discharge thyristor T1.

2. The transcranial magnetic stimulation output circuit according to claim 1, characterized in that, The charging compensation circuit also includes a diode D2 and a resistor R5. The diode D2 and the resistor R5 are connected in series and then in parallel across the two ends of the resistor R4. The anode of the diode D2 is connected to the positive terminal of the power supply, and the cathode of the diode D2 is connected to one end of the resistor R5.

3. The transcranial magnetic stimulation output circuit according to claim 1, characterized in that, The input circuit of the thyristor protection detection circuit OPT1 is connected in parallel across the two ends of the resistor R1. OPT1 is an optocoupler used to transmit the voltage signal across the resistor R1 to the microcontroller MCU after electrical isolation by the optocoupler.

4. A control method for a transcranial magnetic stimulation output circuit, characterized in that, The transcranial magnetic stimulation output circuit according to any one of claims 1 to 3 comprises: During charging, a driving voltage is first applied to the control terminal of the charging start-up drive transistor Q2. After the charging start-up drive transistor Q2 is turned on, it charges the charging capacitor C1. When charging is finished, the charging start-up drive transistor Q2 is turned off, and the induced voltage of the helmet coil L1 charges the compensation capacitor C3 and the charging capacitor C1. When the energy discharge of the helmet coil L1 ends, the compensation capacitor C3 releases energy to the helmet coil L1; after 1 / 4 of the resonance cycle of L1 and C3, an on-control signal is applied to the capacitor discharge thyristor T1, and the capacitor discharge thyristor T1 is turned on, and the charging capacitor C1 will discharge to the helmet coil L1 through the capacitor discharge thyristor T1.

5. The control method according to claim 4, characterized in that, By controlling the turn-on time of the capacitor discharge thyristor T1 to match the discharge time of the compensation capacitor C3, the compensation capacitor C3 and the charging capacitor C1 discharge superimposedly on the helmet coil L1, forming a steep pulse with a combined current rising edge on the helmet coil L1.

6. The control method according to claim 4, characterized in that, When the capacitor discharge thyristor T1 is about to turn on, an opening control voltage is applied to the gate of the thyristor protection device Q1 to turn on the thyristor protection device Q1. The conduction time of the thyristor protection device Q1 is slightly longer than that of the capacitor discharge thyristor T1. After the thyristor protection device Q1 is turned on, resistors R1, R2, and R3 are connected in parallel with the capacitor discharge thyristor T1 to absorb the positive and negative overvoltage peak pulses of the capacitor discharge thyristor T1.

7. The control method according to claim 4, characterized in that, The charging and discharging current on the charging capacitor C1 is led out through the secondary terminal Ciout of the current transformer B1 connected in series in the circuit of the charging capacitor C1; the current led out through the secondary terminal Ciout of the current transformer B1 is obtained by linear rectification and smoothing circuit to obtain the current detection when the charging capacitor C1 discharges to the helmet coil L1, which is used for real-time current sampling and overcurrent protection sampling signal when the helmet coil L1 is working.

8. The control method according to claim 7, characterized in that, The charging and discharging current on the helmet coil L1 is led out through the secondary terminal Liout of the current transformer B2 connected in series in the helmet coil L1 circuit; the current led out through the secondary terminal Liout of the current transformer B2 is converted and used as the current, time and phase detection of the inductance of the helmet coil L1.

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