Posted on Leave a comment

Maplin/Refrakta Torch Modification & Mode Removal

The multimode dimming/flashing modes on Chinese torches have irritated me for a while. If I buy a torch, it’s to illuminate something I’m doing, not to test if people around me have photosensitive epilepsy.

Looking at the PCB in the LED module of the torch, a couple of components are evident:

LED Driver PCB
LED Driver PCB

There’s not much to this driver, it’s simply resistive for LED protection (the 4 resistors in a row at the bottom of the board).
The components at the top are the multimode circuitry. The SOT-23 IC on the left is a CX2809 LED Driver, with several modes. The SOT-23 on the right is a MOSFET, for switching the actual LED itself. I couldn’t find a datasheet for the IC itself, but I did find a schematic that seems to match up with what’s on the board.

Schematic
Schematic

Here’s that schematic, the only thing that needs to be done to convert the torch to single mode ON/OFF at full brightness, is to bridge out that FET.

Components Desoldered
Components Desoldered

To help save the extra few mA the IC & associated circuitry will draw from the battery, I have removed all of the components involved in the multimode control. This leaves just the current limiting resistors for the LED itself.

Jumper Link
Jumper Link

The final part above, is to install a small link across the Drain & Source pads of the FET. Now the switch controls the LED directly with no silly electronics in between. A proper torch at last.

Posted on Leave a comment

Wouxun KG-UV950P Teardown & Analysis

Following on from my review, here are some internal views & detail on the components used in this radio. Below is an overview of the main PCB with the top plate removed from the radio.

Cover Removed
Cover Removed
RF Final Amplifier Stage
RF Final Amplifier Stage

Most visible are these MOSFETs, which are Mitsubishi RD70HVF1 VHF/UHF power devices.  Rated for a maximum of 75W output power at 12.5v (absolute maximum of 150W, these are used well within their power ratings. They are joined to the PCB with heavy soldering, with bypass caps tacked right on to the leads.

RF Pre Drivers
RF Pre Drivers

Here is the RF pre-driver stage, with intermediate transistors hidden under the small brass heatspreader.

Power Section
Power Section

In the top left corner of the radio, near the power input leads, is the power supply & audio amplifier section. Clearly visible are the pair of LA4425A 5W audio power amplifier ICs, these drive the speakers on the top of the radio. Either side of these parts are a 7809 & a 7805 – both linear regulators providing +9v & +5v logic supplies respectively. The large TO220 package device is a KIA378R08PI 3A LDO regulator with ON/OFF control, this one outputs +8v. Just visible in the top right corner are the sockets for the speaker connections.

DTMF Circuits
DTMF Circuits

Here are the two ICs for dealing with DTMF tones, they are HM9170 receivers.

Glue Logic
Glue Logic

In the corner next to the interface jack, there are some CD4066B Quad Bilateral switches. These make sense since the interface jack has more than a single purpose, these will switch signals depending on what is connected.

RF Section
RF Section

Here are visible the RF cans for the oscillators, the crystals visible next to the can at the top. The shields are soldered on, so no opening these unfortunately.
Also visible in this image is a CMX138A Audio Scrambler & Sub-Audio Signalling processor. This IC deals with the Voice Inversion Scrambling feature of the radio, & processes the incoming audio before being sent to the modulator.

Output Filter Network
Output Filter Network

Shown here is the RF output filter network, this radio uses relays for switching instead of PIN diodes, I imagine for cost reasons. The relay closest to the RF output socket has had a slight accident 🙂 This is slated to be replaced soon.

RF Output Jack
RF Output Jack

Finally, the RF output jack.

Audio Speakers
Audio Speakers

Here the speakers are shown, attached to the bottom of the top plate. They are both rated 8Ω 1W.

Posted on 2 Comments

Active Ultracapacitor Balancing

Here’s another active balancing circuit for large ultracapacitor banks, this one is designed for a series string of 6, at 2.5v per capacitor.

Based on the design here, I have transcribed the circuit into Eagle & designed a PCB layout.

Ultracap Balancer Circuit
Ultracap Balancer Circuit – Click to Embiggen

As can be seen from the circuit diagram above, this is just 6 copies of the circuit from the above link, with screw terminals to attach to the capacitor string.

Ultracap Balancer PCB
Ultracap Balancer PCB

And here’s the PCB. the MOSFETs & OpAmps are very small SMT parts, so require a steady hand in soldering. This board can easily be etched by hand as there’s only 3 links on the top side. No need for a double sided PCB.

As always, the Eagle project files & my Eagle library collection are available below: