The difference between the principles of DLP projector and 3LCD projector

There are two common types of home projectors: single DLP and 3LCD. Single DLP projection is a time-sharing reflective projection that uses a single-channel DLP chipset from Texas Instruments (TI), while 3LCD is a simultaneous transmissive projection with three LCD panels represented by Japanese companies such as Epson. The internal structure of a 3LCD projector is relatively complex, so let's briefly introduce the principle. The light source is first polarized to convert all transverse waves in the light source into longitudinal waves (because the liquid crystal it uses can only pass longitudinal waves), and then the light is evenly distributed through an integral lens array. Next, it passes through a dichroic mirror (also called a dichroic mirror) to produce red light and its complementary color cyan light. The red light is reflected by the mirror, and the cyan light is then decomposed into green light and blue light by a second dichroic mirror, thus forming three beams of RGB light. The red and blue lights are reflected by the corresponding mirrors (green light itself is reflected, so no mirror is needed) together with the green light, respectively, to three light-transmitting LCD screens that intersect at right angles (typically, the HTPS LCD screen used by Epson has strong light transmittance). A reflective array that shortens the optical path of the blue light and a dichroic prism (Figure 8) are also needed. Finally, the light formed by the three LCD screens is converged to the lens through the dichroic prism and then projected onto the screen.
Figure 8 Demonstration of color separation prism
Green light needs to be transmitted, and red and blue light are incident vertically and need to be reflected, so ordinary reflectors cannot be used directly here. Only color separation mirrors can be used to form a prism, which reflects red and blue light while transmitting green light to synthesize colors. Therefore, color separation prism is based on its principle; and some people also call it color combination prism, which is based on its purpose. It seems to contradict each other, but it is actually the same thing. It is estimated that some people still do not understand why the last prism is called color separation prism when it is obviously used to synthesize colors. You may as well think that it can be used in reverse, so either name is probably fine, of course, the former name is generally used.
Single DLP type projection is relatively simpler. After passing through the laser, the light source is incident on the filter of the color wheel, at which time the RGB three-color light is formed in time division, and then evenly distributed through the integrator (some models use relay mirrors instead of integrators to reduce costs and volume) and incident on the DMD chip after passing through the TIR prism (Total Internal Reflection Prism). There is a square area on the DMD chip covered with tiny aluminum reflectors at the pixel level, which are reflected to the lens group and finally projected onto the screen. By controlling the rotation angle of the reflector on the DMD through the circuit, different grayscales can be obtained, and then combined with the RGB color generated by the filter, the color is superimposed using the visual residual characteristics of the human eye, and finally the color picture we see is formed. This is the working principle of single-chip DLP. In fact, there are also high-end models that use 3 DMD chips at the same time. Because they are not included in the common consumer-grade models and the internal structure is too complicated, they are not involved here.
Therefore, the reason why the internal structure of a single DLP is simple is not only because there is only one DMD chip instead of three LCDs, but the most important thing is that the most complex structure and the most core functions are all handled by the DMD chipset itself, so when we disassemble it, we will feel that DLP is much "simple". But in fact, the DMD chipset is very complex. Due to the limited space of this article, it is expected that the chipset will be placed in the third article.
In addition, there are also many types of light sources for single DLP projection, including three-color LED, single/dual-color laser + phosphor (generally called Laser-phosphor), three-color laser (RGB laser), and the most common ultra-high pressure mercury lamp (such as Philips UHP) bulb light source. In addition, there are also mixed types of light sources, such as laser + LED light source, or UHP + UHP dual light source superposition, etc.