Cant get LM2917 working - Electronic Circuits Projects Diagrams Free

vuchris · 27th August 2007, 12:22 PM

Hi I'm in the middle of making a frequency to voltage converter. I have an incremental encoder hooked onto my DC motor which spins at a max no load speed of about 3500 RPM (about 58hz).

I'm using the 16 pin package of the LM2917 freq to voltage converter IC, the data sheet for it is below:
http://cache.national.com/ds/LM/LM2907.pdf

My circuit is below, exactly as it appears on a breadboard:

http://aycu20.webshots.com/image/257...5476756_rs.jpg

I pumped 15V to VCC and had the incoder pulsing slowly (motor was turning slow), and the chip just heated up like crazy. I had VCC=5V and Vout just gave me 5V, so in other words VCC=Vout. Did I wire something wrong here? I think I've wired it according to "Minimum component tachometer" figure on page 8 of the data sheet.

Thanks

Roff · 27th August 2007, 09:58 PM

You will, or already have, burn out the internal zener if you put 15V across it. Read the datasheet, especially the part about USING ZENER REGULATED OPTIONS (LM2917).
The datasheet doesn't appear to characterize the part with Vcc<6V.
EDIT: Also read the section, CHOOSING R1 AND C1. I think C1=22pF is way too low.

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27th August 2007, 12:22 PM	(permalink)
vuchris	Cant get LM2917 working Hi I'm in the middle of making a frequency to voltage converter. I have an incremental encoder hooked onto my DC motor which spins at a max no load speed of about 3500 RPM (about 58hz). I'm using the 16 pin package of the LM2917 freq to voltage converter IC, the data sheet for it is below: http://cache.national.com/ds/LM/LM2907.pdf My circuit is below, exactly as it appears on a breadboard: http://aycu20.webshots.com/image/257...5476756_rs.jpg I pumped 15V to VCC and had the incoder pulsing slowly (motor was turning slow), and the chip just heated up like crazy. I had VCC=5V and Vout just gave me 5V, so in other words VCC=Vout. Did I wire something wrong here? I think I've wired it according to "Minimum component tachometer" figure on page 8 of the data sheet. Thanks

27th August 2007, 09:58 PM	(permalink)
Roff	You will, or already have, burn out the internal zener if you put 15V across it. Read the datasheet, especially the part about USING ZENER REGULATED OPTIONS (LM2917). The datasheet doesn't appear to characterize the part with Vcc<6V. EDIT: Also read the section, CHOOSING R1 AND C1. I think C1=22pF is way too low. __________________ Ron (aka Rube) Last edited by Roff; 27th August 2007 at 10:12 PM.