# Generating positive and negative voltages for gate drive signals

#### SiCEngineer

Joined May 22, 2019
320
I am looking at a schematic design from GaN systems https://gansystems.com/wp-content/uploads/2018/10/Schematic-Prints-GS66508T-EVBDB2-180830.pdf, which uses a DC/Dc converter called https://www.mouser.co.uk/datasheet/2/468/R1DX-1710005.pdf to generate +6 and -4V from a 5V voltage input. The data sheet says the voltage is +/-5V, and the schematic uses a 6V Zener diode and a 1K resistor to split the voltage into +6/-4V.

My question is,if the output voltage is only a max of +5V, how are they generating a 6V positive rail? It is something to do with the +/- voltage generation of the converter? My second question is what is the purpose of the resistor? I understand the diode voltage gives the 6V but how do we calculate the R value to ensure -4V is generated alongside it?

#### AlbertHall

Joined Jun 4, 2014
11,529
The DC/DC converter has an isolated output so, for instance, you could connect the -5V output to a +12V source then the converter outputs would be +12V, +17V, and +22V (still 10V across the three outputs).

In the circuit shown, a 6V zener and resistor are connected across the converter outputs. Now from the junction of the resistor and zener you have +6V and -4V measured relative to the diode/resistor junction. Those relative voltages remain the same whatever you connect that junction to (like the with the 12V supply above) so if the junction is connected to 0V then you will have +6V and -4V supply rails.

For the selection of the resistor see: https://www.electronics-tutorials.ws/diode/diode_7.html?utm_referrer=https://www.google.com/

• SiCEngineer

#### SiCEngineer

Joined May 22, 2019
320
The DC/DC converter has an isolated output so, for instance, you could connect the -5V output to a +12V source then the converter outputs would be +12V, +17V, and +22V (still 10V across the three outputs).

In the circuit shown, a 6V zener and resistor are connected across the converter outputs. Now from the junction of the resistor and zener you have +6V and -4V measured relative to the diode/resistor junction. Those relative voltages remain the same whatever you connect that junction to (like the with the 12V supply above) so if the junction is connected to 0V then you will have +6V and -4V supply rails.

For the selection of the resistor see: https://www.electronics-tutorials.ws/diode/diode_7.html?utm_referrer=https://www.google.com/
Okay, that's making a lot more sense now. So the converter having +5/-5V outputs means it essentially generates 10V across its two outputs, and I can do with that as I please to generate different voltages?

If I may also ask. What is the purpose of the LED's attached to the output of the converter?

Thanks!

#### AlbertHall

Joined Jun 4, 2014
11,529
The LEDs are, as far as I can see, just to tell you that it is alive.
A harder question is why they use two 3.3k resistors in parallel to control the LED current and I have no useful answer to that.

• SiCEngineer