UC2625-EP
www.ti.com .................................................................................................................................................................................................. SLUS802–MARCH 2008
Fast High-Side N-Channel Driver with Transformer Isolation
A small pulse transformer can provide excellent isolation between the UC2625 and a high-voltage N-Channel
MOSFET while also coupling gate drive power. In this circuit (shown in Figure 13), a UC3724 is used as a
transformer driver/encoder that duty-cycle modulates the transformer with a 150-kHz pulse train. The UC3725
rectifies this pulse train for gate drive power, demodulates the signal, and drives the gate with over 2-A peak
current.
+12V
VMOTOR
3
33kW
6
4
7
8
PUA
2
4
7
UC3724N
UC3725N
1:2
8
1
2
5
1
6
3
5kW
1nF
100nF
TO MOTOR
Figure 13. Fast High-Side N-Channel Driver with Transformer Isolation
Both the UC3724 and the UC3725 can operate up to 500 kHz if the pulse transformer is selected appropriately.
To raise the operating frequency, either lower the timing resistor of the UC3724 (1 kΩ min), lower the timing
capacitor of the UC3724 (500 pF min) or both.
If there is significant capacitance between transformer primary and secondary, together with very high output
slew rate, then it may be necessary to add clamp diodes from the transformer primary to 12 V and ground.
General purpose small signal switching diodes such as 1N4148 are normally adequate.
The UC3725 also has provisions for MOSFET current limiting. See the UC3725 data sheet for more information
on implementing this.
Copyright © 2008, Texas Instruments Incorporated
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