High Voltage Current Switch Startup Protection Circuit
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Solution Overview
Problem
Conventional driver circuits with high voltage transistors, such as DMOS, face challenges in fully turning off external transistors during startup due to high breakdown voltage, risking damage from initial start-up current.
Innovation Solution
A bias generation circuit generates a bias current that is mirrored and amplified through a current mirror to sink into nodes shared by internal reference voltage and the gate of high voltage transistors, ensuring both nodes are in a logic state to turn off the transistors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional enable signal is used to control the driver circuit, then the driver can be enabled or disabled during normal operation, but the external transistor cannot be fully turned off during startup due to high breakdown voltage in DMOS transistors
Solution Approach 1:
The circuit performs preliminary action by forcing the gate voltage to a defined logic state before the internal power supply is ready. The bias generation circuit and current mirror are activated during startup to preemptively establish the correct gate voltage state, preventing the external transistor from turning on before it should be protected.
Solution Approach 2:
An intermediary circuit is introduced between the internal power supply and the gate of the high voltage transistor. This intermediary bias generation circuit includes a current mirror that decouples the gate control from the unstable startup power supply, providing a stable control path that operates independently during the critical startup period.
2Power
If high voltage power supply is used to enable the driver circuit, then the driver can operate at high voltage, but the gate node cannot be properly controlled during startup when internal power supply is not ready
Solution Approach 1:
The power supply control is segmented into two independent paths: a high voltage power supply path for the main driver operation, and a separate low voltage bias generation path for gate control during startup. This segmentation allows each path to operate independently with appropriate voltage levels, solving the conflict between high voltage operation and startup control.
Solution Approach 2:
The circuit changes the voltage parameter of the gate control path during startup. Instead of using the high voltage power supply directly, the circuit switches to a low voltage bias generation mode during startup, then transitions to normal high voltage operation mode once the internal power supply is ready, effectively adapting the control parameters to the operational phase.
3Productivity
If DMOS transistors are used in the driver circuit, then high voltage operation is enabled with low on-resistance, but the transistors cannot be fully turned off during startup due to high breakdown voltage
Solution Approach 1:
The circuit applies preliminary anti-action by preemptively forcing the gate voltage to the correct state before the harmful start-up current can flow. The bias generation circuit and current mirror are activated to counteract the potential damage before it occurs, preventing the external transistor from being damaged by start-up current.
Solution Approach 2:
An intermediary bias generation circuit is introduced between the power supply and the DMOS transistor gate. This intermediary provides a controlled voltage path that decouples the high voltage operation benefits from the startup control problems, allowing the DMOS transistor to operate at high voltage with low on-resistance while being protected during startup by the separate bias control path.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Effectively prevents damage to external transistors by ensuring they are fully turned off during startup, even when the internal power supply is not ready to supply voltage, thereby protecting the circuit.
Implementation Method 1
The bias current is mirrored by a current mirror containing a first plurality of transistors to a first one of a second plurality of transistors. The first one of the second plurality of transistors may amplify the mirrored bias current and transmit the amplified bias current to a second one of the second plurality of transistors.
Data Source
AI summary
In a current switch, a bias generation circuit electrically connected to a high voltage power supply generates a bias current. The bias current is mirrored by a current mirror containing a first plurality of transistors to a first one of a second plurality of transistors. The first one of the second plurality of transistors amplifies the mirrored bias current and transmits the amplified bias current to a second one of the second plurality of transistors. The second one of the second plurality of transistors sinks the amplified bias current into a node shared by an internal reference voltage, thereby putting the node in a first logic state. A third one of the second plurality of transistors receives the amplified bias current from the second one of the second plurality of transistors and sinks the amplified bias current into a node shared by a gate of a high voltage p-type transistor, thereby putting the node in the first logic state. Putting both nodes in the first logic state turns off the high voltage transistor.