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Current sampling circuit

A current sampling and voltage sampling technology, applied in electrical components, adjusting electrical variables, converting DC power input to DC power output, etc., can solve the problems of high power consumption, limitation, and temperature rise of current sampling resistors

Inactive Publication Date: 2018-02-16
MORNSUN GUANGZHOU SCI & TECH
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

[0004] However, when the primary side current of the isolated converter increases, the above-mentioned current sampling circuit has the problem of large power consumption of the current sampling resistor R1. When the product power is large, more resistors need to be used in parallel. This leads to problems such as low product efficiency, temperature rise, cost increase, and increased layout space occupied. The application of this current sampling circuit in high-power isolated converters or low-power products with high power density is limited.

Method used

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Examples

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no. 1 example

[0024] Figure 4 A schematic diagram of the first embodiment is shown, and its power stage topology is a flyback topology. The flyback topology circuit includes a transformer T1, an N-MOS transistor Q1, a first diode D1, and a first capacitor C1. The transformer includes a first primary winding and a first secondary winding; the flyback circuit The connection relationship is as follows: the opposite end of the first primary winding is connected to the positive pole of the power input, the same end of the first primary winding is connected to the drain of the N-MOS transistor Q1, and the N-MOS The source of the tube Q1 outputs current to the current sampling circuit of the present invention; the terminal with the same name of the first secondary winding is connected to the anode of the first diode D1, and the cathode of the first diode D1 is connected to the output terminal positive pole, the opposite end of the first secondary winding is connected to the negative pole of the ...

no. 2 example

[0029] Figure 5 The schematic diagram of the second embodiment is shown, and its power stage topology is a flyback topology. The difference from the first embodiment is that the DC bias circuit connects the second resistor and the first resistor through a constant current source IC2 The voltage generated above is realized, the anode of the constant current source IC2 is connected to the positive pole of the power input, and the cathode of the constant current source IC2 is connected to the first terminal of the second capacitor C2, that is, the cathode of the constant current source IC2 is connected to the first terminal of the second capacitor C2. Control the current sampling pin of IC.

[0030] The working principle is: the output current of the constant current source flows through R2 and R1. Since the output current of the constant current source is relatively stable, the voltage drop generated on R2 and R1 is also relatively stable, so that the same as the implementation...

no. 3 example

[0032] On the basis of the first embodiment and the second embodiment, a voltage feedforward circuit is added, which is connected between the positive pole of the power input and the current sampling pin CS of the control IC.

[0033] The voltage feedforward circuit of the present invention includes a third resistor R3, the first terminal of R3 is connected to the positive pole of the power input, and the second terminal of R3 is connected to the first terminal of R2.

[0034] When the input voltage is not fixed or the input voltage range is wide, the product overcurrent point can be adjusted through the first resistor, the third resistor combined with the fourth resistor and the second resistor, or by The first resistor and the third resistor are adjusted in combination with the constant current source IC2 and the second resistor, so that the overcurrent point of the product is relatively stable within the input voltage range, and at the same time, it can be compared with the ...

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Abstract

The invention discloses a current sampling circuit, which can be applied to primary side current sampling of topology of a flyback converter, a forward converter and the like, and through prebias of direct voltage at a current sampling pin of a control IC, sampling voltage of a primary side current sampling resistor can be greatly reduced. The current sampling method can remarkably reduce the value of resistance and power dissipation of the sampling resistor, improve product efficiency and product power density, and broaden the application fields of directly performing primary side current sampling through a power resistor, and the circuit is easy to implement and practical.

Description

technical field [0001] The invention relates to a primary side current sampling circuit of an isolation converter, in particular to a primary side current sampling circuit of a flyback converter. Background technique [0002] For isolated converters with low power, such as DC / DC converters with output power less than 10W, due to cost and volume constraints, it is not suitable to use transformers and other primary side current sampling schemes with complex circuits or large footprints . Traditional solutions such as figure 1 As shown, by connecting the power resistor in series with the input ground under the main power N-MOS tube of the flyback converter, the primary current is sampled directly through the power resistor, and then input to the primary current sampling of the control IC after low-pass filtering At the same time, in order to ensure the consistency of the overcurrent point of wide input voltage products, a voltage feedforward that is inversely proportional to ...

Claims

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Application Information

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IPC IPC(8): H02M3/335
CPCH02M3/335H02M1/0009
Inventor 李湘卢泽伟阮启钦刘海霞
Owner MORNSUN GUANGZHOU SCI & TECH
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